1. Field of the Invention
The invention relates to a cladding tube of a zirconium alloy especially for a nuclear reactor fuel rod and method for fabricating the cladding tube.
2. Description of the Prior Art
Such cladding tubes must meet stringent requirements especially with respect to the so-called "stress corrosion". This stress corrosion involves a corrosion mechanism on the inside of the cladding tube in the nuclear reactor, for which expansion of the cladding tube due to swelling of the filled-in nuclear fuel and nuclear fission products liberated by the nuclear fuel such as iodine are responsible. Stress corrosion plays a particular role in nuclear reactor fuel rods which are inserted into boiling-water nuclear reactors. There, particularly abrupt power changes of the nuclear reactor can lead to a breakthrough of the cladding tube walls of the nuclear reactor fuel rod due to stress corrosion.
It is known from German Published Prosecuted Application (DE-AS) No. 25 50 029 to provide cladding tubes of a zirconium alloy for nuclear reactor fuel rods with an inner lining of highest-purity zirconium in order to avoid stress corrosion. This inner lining is obtained by co-extrusion of the cladding tube blank with a tube of highest-purity zirconium which is inserted into the bore of the cladding tube blank and has been welded there to the cladding tube blank. Highest-purity zirconium is a very expensive material. In addition, the tube of high-zirconium must be fitted very accurately into the bore of the cladding tube blank if an acceptable metallurgical joint between the high-purity zirconium and the zirconium alloy of the cladding tube is to take place in the subsequent co-extrusion. A cladding tube of zirconium alloy lined with high-purity zirconium on the inside, can therefore be obtained only by an elaborate and expensive process.